Arsenal have Manuel Almunia to thank for keeping their European dream alive on a fruitless night at Old Trafford.

The Spanish goalkeeper pulled off a string of superb saves to thwart Manchester United but he could not deny the holders a deserved lead at the halfway stage of this Semi-Final.

John O’Shea converted from close range after 18 minutes to reward United’s flying start to the first leg but the hosts could not add to their lead. They came mighty close though, Cristiano Ronaldo thumping the bar from long range.

Emmanuel Adebayor fired Arsenal’s best chance over the bar but the visitors could not manage the away goal they craved. Nonetheless, they are still in the tie. Now it’s all back to the Emirates in six days’ time for the conclusion of this all-English classic.

Arsčne Wenger had two decisions to make before the kick-off. Who would partner Kolo Toure in defence? And how would he shuffle his attacking pack in the absence of Andrey Arshavin? In the event Mikael Silvestre (back) and Kieran Gibbs (ankle) both passed fitness tests; the former got the nod ahead of Johan Djourou while the latter continued his crash course in top-level football up against the World Player of the Year, Ronaldo. Further forward Cesc Fabregas played just off Adebayor while Samir Nasri partnered Alex Song in the centre of midfield.

Arsenal and Manchester United had never met in a European fixture before tonight and the stakes could barely be higher. Old Trafford was crammed and the atmosphere befitted the occasion – a cacophony of noise greeted the teams as they emerged on a sunlit Spring evening.

First legs are traditionally cagey affairs but pre-match murmurings suggested that this might be an exception to the rule. Both sides are renowned for attacking football; both sides have looked vulnerable at the back in recent weeks.

According to Wenger, Arsenal would be “audacious” in their pursuit of an away goal but that would have to wait while the visitors weathered an early United storm. Only 70 seconds had elapsed when Wayne Rooney climbed above Bacary Sagna to send a looping header towards the far corner. Almunia clawed it away. Moments later a Gibbs slip let in Ronaldo but, to the teenager’s relief, the Portuguese star lashed his shot across goal.

Arsenal needed a foothold in the game but United would not let up.

Almunia made a wonderful double save to deny Carlos Tevez from close range after 15 minutes but, within 60 seconds, the Spaniard was picking the ball out of the back of his net. Michael Carrick collected a half-cleared corner just inside the area and Silvestre could only poke his cut-back into the path of O’Shea. The right-back made no mistake from eight yards to give United a deserved lead.

These were worrying times for Arsenal – the pace and power of United’s attacks was awesome at times – but they finally got a sight of goal in the 26th minute. Theo Walcott span away from Patrice Evra and fed Adebayor, who laid the ball back for Fabregas. The captain’s strike was fierce and low, but Edwin van der Sar got down well to save.

His opposite number was soon back in action – and how. Almunia’s heroics continued with another point-blank save to keep out Ronaldo’s header from Tevez’s right-wing cross. Then the Spaniard gathered at the second attempt when United’s No 7 had another go.

A goal then might have left Arsenal dead and buried. Instead, you could just about see the green shoots of recovery. The visitors got the measure of United’s midfield and, with Abou Diaby prominent, they began to probe patiently.

Carving out chances was another matter entirely.

Adebayor had his first sight of goal just after the hour mark, chesting down past Rio Ferdinand and hammering a shot over the bar. And Fabregas screwed a shot wide after from just inside the box after one of many slick counter-attacks.

But United were just as threatening. Anderson should have done better when presented with an opportunity on the edge of the box and Ronaldo crashed a shot against the bar from 25 yards. For once, Almunia could do nothing but watch.

Ryan Giggs, making his 800th appearance for United as a sub, had the ball in the net with 12 minutes left but his celebrations were cut short by an offside flag.

Wenger brought Nicklas Bendtner and Eduardo into the fray in search of the goal that would alter the complexion of the tie. The Dane almost did the trick, beating Van der Sar to Fabregas’ free-kick but failing to direct his header on target.